FIG. 6 shows the general construction of a conventional EB type IC tester. Reference numeral 10 denotes an electron beam irradiation unit. The electron beam irradiation unit 10 is provided with a vacuum vessel called a body tube, in which an electron gun, an acceleration electrode, a focusing coil, a deflecting coil, etc. are mounted, though not shown, and an electron beam is emitted from the underside 11 of the electron beam irradiation unit. Accordingly, the underside 11 will hereinafter be referred to as an electron beam emitting face.
The electron beam irradiation unit 10 is mounted on a movably held support table 20. The support table 20 is pivotally secured to a column 30 in this example and hence is allowed to swivel about the column 30. By this swivel movement the electron beam irradiation unit 10 can be removed front its normal position just above a test head 40 forming the IC testor, enabling an IC under test to be loaded into and unloaded from an IC socket on a support plate 51 from above. The support table 20 is supported in such a manner that it is also movable up and down along the column 30. Incidentally, the electron beam irradiation unit 10 is loaded on an X-Y driving stage 12 on the support table 20 so that the point of irradiation by an electron beam can be moved in the X-Y direction.
The support table 20 has a cavity 21, which receives the electron beam emitting face 11 of the electron beam irradiation unit 10. In the bottom plate of the support table 20 there is made a round hole 22 opposite the electron beam emitting lace 11, and a cylindrical member 23A is received in the round hole for connecting the electron beam irradiation unit to the test head 40. The lower open end of the cylindrical member 23A is closed with an insulating plate 23B called a barrier board, by which the interiors of the cavity 21 and the cylindrical member 23A are hermetically sealed and kept vacuum.
An IC under test 50 is placed opposite the electron beam emitting face 11. The IC under test 50 is secured to the IC socket 52 (FIG. 1) mounted on the top of the support plate 51 centrally thereof. On the underside of the support plate 51 there are formed wiring conductors connected to respective terminals of the IC socket and extended radially for connection to contact pads provided at the marginal edges of the support plate 51, though not shown. Elastic contactors 53A, called "pogo pins" which are planted on a connection board 53 supported on the top of a column 54, are elastically urged against the contact pads.
The elastic contactors 53A on the connection board 53 and conductor pins 23C planted through the barrier board 23B are interconnected by impedance-matched cables 24 such as coaxial cables. The conductor pins 23C on the barrier board 23B and contact pads provided on a performance board 25, though not shown, are elastically interconnected by elastic contactors 55A planted on a connection board 55 and projecting out therefrom upward and downward, and the contact pads on the performance board 25 are connected to the test head 40. Thus the cylindrical member 23A and the support plate 51, the connection board 53, the column 54, etc. disposed inside the cylindrical member are supported on the performance board 25. The IC under test 50 is fitted into the IC socket from above after the support table 20 is disconnected from the cylindrical member 25A and turned away therefrom.
The inside of the cylindrical member 23A in which the coaxial cables 24 are disposed is evacuated; in general, however, the coaxial cable has a shortcoming that, when placed in a vacuum, it evolves gas and hence impairs the degree of vacuum in the cavity 21. Moreover, since the support table 20 and the test head 40 are mechanically connected by the cylindrical member 23A, vibration of a fan motor for air cooling, provided in the test head 40, for example, is introduced to the support table 20, and consequently, the position of irradiation by the electron beam oscillates, decreasing the resolution of the potential distribution image of the integrated circuit by the detected secondary electrons.
Furthermore, since the support table 20 is air-tightly connected to the top of the cylindrical member 23A and has its height fixed relative to the performance board 25, the height of the electron beam emitting face 11 relative to the support plate 51 is also fixed. As the result of this, the spacing Z (hereinafter referred to as a working distance) between the IC under test 50 and the electron beam emitting face 11 is fixed and cannot be adjusted. Accordingly, even if the thickness of the IC under test 50 and the thickness of the IC socket change, the working distance cannot be adjusted to maximize the resolution of the image by the detected secondary electrons, and hence the test cannot always be made under the condition of optimum resolution. Besides, the lower open end of the cylindrical member 22 is closed with the barrier board 23B but the hermetic seal by the barrier board 23A is not so reliable table.
A first object of the present invention is to provide an EB type IC tester which does not allow easy deterioration of the degree of vacuum of the electron beam emitting portion.
A second object of the present invention is to provide an EB type IC tester which attains the above-noted first object and permits adjustment of the working distance between the electron beam emitting face and the IC under test.
A third object of the present invention is to provide an EB type IC tester which attains the above-noted first object and does not allow easy transmission of vibration from the test head to the IC under test and the electron beam irradiation unit.